In a field of display technology, for example, in a liquid crystal display or an organic electroluminescent display device, a thin film transistor is a basic component of an array substrate. The characteristics of the films of the thin film transistor affect the electrical performance of the thin film transistor, and thus affect the final display effect of the display devices.
Square resistance is an important means of evaluating film properties. At present, square resistance is usually measured by a four-probe method. Tests are performed by means of four probes with equidistant and aligned in a straight line, and the four probes are in contact with the film to be tested directly. For example, FIG. 1 is a schematic diagram for testing square resistance. The detector comprises four probes, and distances between any adjacent probes are equal. In a case that the probes are pressed on a conductive film material, the square resistance of the material is illustrated by the resistance meter, and the principle is that the two probes at two outer ends produce a current field and the two probes at the inner side test a potential difference formed by the current field on the two inner probes. The larger the resistance is, the greater the potential difference is, so that the square resistance of the film to be tested is measured.